Universal Adaptive Control via Output Feedback for Nonlinear Systems with Parametric and Measurement Uncertainty

The problem of global state regulation via output feedback is studied for a class of nonlinear systems with unknown parameters in the state and output equations. In contrast to the existing results, both the value and sign of the unknown parameter in the system output are not required to be known a priori. Moreover, the controlled plant is assumed to be nonlinearly dependent of the output and the unknown parameters but linearly in the unmeasured states, with a lower-triangular structure. Using the idea of K-filter, we first construct a nonlinear observer with a dynamic-gain for the uncertain system. We then develop, by virtue of the universal control philosophy with a Nussbaum function, a universal adaptive control scheme that achieves global state regulation and boundedness of the closed-loop system.